It has been recognized that the delivery of oxygen and oxygen-enriched air to the respiratory tract of a patient often results in discomfort to the patient, especially when the air is delivered over an extended period of time. It has also been recognized that the delivery of air having relatively low absolute humidity can result in respiratory irritation.
Several devices have been proposed to overcome these problems. U.S. Pat. No. 4,632,677, issued to Richard H. Blackmer, the disclosure of which is incorporated herein by reference, describes an oxygen-enriching apparatus including means for increasing or regulating the humidity of the air. The Blackmer apparatus employs an array of membrane cells, a vacuum pump to draw a flow of humidity-and-oxygen-enriched air from each cell, low- and high-temperature condensers connected to receive air drawn from the cells, and a proportioning valve connected to the condensers for providing a desired humidity level of the air.
According to the Blackmer '677 patent, air supplied to the patient may be heated by circulation of warm air over delivery tubing, use of electric resistance heaters, and circulating warm liquid co-linearly with the delivery tubing. With regard to warm liquid heating, warm water is circulated through a tubing jacket comprised of feed and return tubes, which trace the delivery air line, by means of a motor-driven pump. A feed tube extends from the pump and a return tube connects to a water reservoir. Regarding warm air circulation, a blower delivers warmed air to a tube which co-axially surrounds the oxygen-enriched air delivery tubing. Electrical resistance heating may also be used according to the Blackmer '677 patent.
Another system is described in U.S. Pat. No. 4,773,410, issued to Richard H. Blackmer et al., the disclosure of which is incorporated herein by reference. The apparatus described by the Blackmer et al. '410 patent includes a permeable membrane to permit a liquid-vapor boundary, as well as means for delivering a substantially condensation-free saturated vapor-gas stream to a respiratory tract. In one embodiment described in the Blackmer et al. '410 patent, the apparatus uses a delivery tube with electrical heating elements that heat the air as it passes through the tube. In another embodiment, a heater heats water which is then delivered through a separate tube that is connected to the delivery tube near the delivery tube's exit port. The heated water then flows counter-current to the air flow to heat the air and exits the delivery tube near its opposite end.
Nevertheless, there remains a need for an improved apparatus for respiratory tract therapy that can be used in various settings including clinical, hospital, and home settings. There also remains a need for improved methods of respiratory tract therapy.